Improving the ability of peak expiratory flow rates to predict asthma.

A major problem in the behavioral management of childhood asthma concerns recognition of the early signs of impending episode. An objective measure commonly used to aid recognition of early warning signs is the peak expiratory flow rate (PEFR). This study examined the ability of PEFRs to predict asthma within a 12-hour period; the prediction method used was based on prior and conditional posterior probabilities. Twenty-five children with asthma recorded their PEFR twice daily, and also recorded the date and time of their asthma episodes. Conditional posterior probabilities and the ratio of hits to misses were computed for each subject at successively lower flow rates. The average improvement in predictability from the prior probability to the highest posterior probability was 491%. The ratio of hits to misses and the number of episodes predicted, however, decreased as the posterior probability increased. Selection of the PEFR at lower posterior probabilities resulted in fewer prediction errors and led to prediction of a higher number of episodes than selection of the PEFR at the highest posterior probability.